This invention relates to a method for adhering to hard tissue. This invention also relates to adhesive compositions for use on hard tissue.
In recent years there has been intense interest in the dental field in adhesives that bond to hard tissues such as dentin. Forces generated by the polymerization contraction of dental restorative materials suggest that a minimum adhesion strength for bonding restorative materials to hard surfaces in in vivo clinical procedures would be desirable. For example, M. Jensen, Polymerization Shrinkage and Microleakage International Symposium on Posterior Composite Resin Dental Restorative Materials, 243-44 (1985) reports a contraction force of 7.3 MPa. for conventional composite materials. In many instances the minimum adhesive strength has not been achieved, resulting in direct communication between dentin and the oral cavity via gaps between the dental restorative material and the cavity walls. This may be responsible, in part, for patient complaints of sensitivity and for pulpal irritation and inflammation. See, Tao, The relationship between dentin bond strengths and dentin permeability Dental Materials, Vol. 5, 133-39 (1989).
Recently a novel priming method was developed in the laboratory of the assignee of this invention and is sold commercially as ScotchBond 2(trademark) Light Cure Dental Adhesive with Scotchprep(trademark) Dentin Primer (commercially available from 3M). This priming method has achieved average shear strengths in vitro in excess of 20 MPa. U.S. Pat. No. 4,719,149 (Aasen et al.) describes that invention as an acid and a water-soluble film former useful for priming hard tissue (e.g., dentin). The acid has a pKa less than or equal to that of phenol. The calcium salt(s) of the acid are soluble in the film former. The film former is exemplified as comprising various difunctional and monofunctional monomers and optional cosolvents with 2-hydroxyethylmethacrylate and water being preferred.
Kusumoto et al., U.S. Pat. No. 4,535,102 discloses an adhesive coating material for a hard tissue comprising (1) a polymer having an acid value of 30 to 700 and including in recurring units a hydrophobic group and two carboxyl groups or one carboxylic anhydride group bonded to the polymer, and (2) a polymerizable vinyl compound or a mixture of said polymerizable vinyl compound and an organic titanate compound.
Engelbrecht et al., U.S. Pat. No. 4,806,381 discloses oligomeric or prepolymeric organic compounds that contain both polymerizable unsaturated groups and acid radicals, their salts or their reactive-derivative radicals. The compounds adhere to biological substrates such as tooth tissue.
Beech et al., U.S. Pat. No. 4,732,943 discloses an adhesive comprising (a) a condensate of xcex5-caprolactone with one or more acrylic monomers containing hydroxy groups and (b) a polymer containing binding groups capable of binding to the dentin.
One major limitation in the prior art has been the difficulty of adhering to hard tissue which is not dry. This necessitates maintaining a dry tooth surface during the priming procedure which is in practice difficult to ensure. For instance, the oral cavity is inherently humid and the hard tissue is susceptible to fluid perfusion from the pulp chamber. The susceptibility of the tooth surface to this fluid perfusion is believed to be a function of the proximity of the prepared surface to the pulp chamber. Near the pulp, the tubules are very close together and the water content of this deep dentin is very high. See, Pashley, Dentin: A Dynamic Substrate Scanning Microscopy, Vol. 3, No. 1, 161-76 (1989).
Additionally, dental materials adhere poorly to sclerotic dentin and cervical enamel. Sclerotic dentin is characterized as hypermineralized dentin (i.e., the dentinal tubular contents are mineralized) and has a coloration that can range from transparent to intense yellow or yellow-brown.
The invention provides a pretreatment (a primer) that is applied directly to the hard tissue. The invention has particular utility for adhering to or coating sclerotic dentin and cervical enamel or for adhering to or coating hard tissue in a high humidity environment. The primer enables formation of extremely strong bonds to dentin (including sclerotic dentin), exhibiting shear strengths as high as 30 MPa., when tested in shear using the procedure described herein. Tests to date indicate that an extremely durable adhesive bond with little or no detectable microleakage can be obtained. The primers of the invention can, if desired, be water-based, thus substantially reducing the need to apply them in a dry field. The primers of the invention work very well in high humidity environments or when bonding to sclerotic dentin.
The present invention provides, in one aspect, a method for adhering to or coating hard tissue,,comprising the steps of:
(a) applying to the hard tissue adhesively effective amounts of an acid and a water-dispersible film former comprising a polymer and
(b) hardening said film former.
For purposes of this invention xe2x80x9chardeningxe2x80x9d is defined as the formation of a covalently or ionically crosslinked polymer as opposed to merely drying a previously prepared polymer of its carrier solvent or merely cooling a previously melted thermoplastic polymer.
The present invention also provides novel primer compositions for use in such method, comprising a mixture of an acid and a film former comprising a polymer prior to the hardening step, said mixture being in the form of a film atop said hard tissue.
In the practice of the present invention, the hard tissues which can be adhered to or coated include human and animal tissues such as teeth (including the component parts which are enamel, dentin, and cementum), bone, fingernails, and hoofs. The invention has particular utility for adhering to or coating dentin, sclerotic dentin, enamel, and cervical enamel.
The acid and film former can be applied to hard tissue concurrently or sequentially. If they are applied sequentially, then if desired the acid can be rinsed from the hard tissue (e.g., using a water rinse) before application of the film former, or the film former can be applied to the acid without an intermediate rinsing step. For brevity, formulations comprising the film former will sometimes be referred to as the xe2x80x9cprimer,xe2x80x9d regardless of whether the concurrent or sequential application method is employed. Thus, when the acid and film former are applied to the hard tissue concurrently, then the acid and film former will sometimes be referred to collectively as the xe2x80x9cprimerxe2x80x9d. When the acid and film former are applied to the hard tissue sequentially, then the acid, if in a solvent, will sometimes be referred to as an xe2x80x9cetchantxe2x80x9d and the film former will sometimes be referred to as the xe2x80x9cprimer.xe2x80x9d
In one method of the invention, the primer is permitted to stand on the hard tissue for a desired period of time, readily volatile cosolvents are removed therefrom (e.g., by air-drying) to modify the surface of the hard tissue and leave a residual film on the surface of the hard tissue (and in the case of dentin to form a xe2x80x9chybrid layerxe2x80x9d with the hard tissue), the residual film is overcoated with a layer of additional film former (the additional film former can be water-soluble or water-insoluble but should preferably form a homogeneous solution when combined with the residual film), then the additional film former and residual film are hardened and optionally overcoated with a composite, restorative, glass ionomer cement, sealant or other hardenable coating (hereafter such composites, restoratives, glass ionomer cements, sealants, and other hardenable coatings will be referred to collectively as xe2x80x9crestorativesxe2x80x9d). As used herein, xe2x80x9csurface modified hard tissuexe2x80x9d refers to hard tissue that has been exposed to the primers of the invention. As used herein, xe2x80x9chybrid layerxe2x80x9d refers to the layer of resin-reinforced dentin that consists of collagen and perhaps hydroxyapatite that is infiltrated and surrounded by the monomers, oligomers and polymers of the film former and the optional additional film former. Thus the invention enables priming of hard tissue in order to improve the bond strength or durability of a restorative or coating applied thereto.
Acids for use in the present invention can be inorganic or organic acids, and if organic can be monomeric, oligomeric or polymeric. If desired, a precursor to the acid such as an acid anhydride, e.g., 4-Methacryloxyethyl Trimellitate Anhydride (4-META), acid halide (including inorganic acid halides such as Lewis acids, e.g., ferric chloride, and organic acid halides), or ester can be used in place of the acid itself, e.g., to generate the desired acid in situ. Suitable acids include mineral acids, carboxylic acids, sulfonic acids, and phenols, with carboxylic acids, alkylsulfonic acids, arylsulfonic acids, and phosphonic acids being preferred.
The acid has a pKa in water that is less than or equal to that of phenol. Preferably, the pKa of the acid is between about xe2x88x9220 and about +10, more preferably between about xe2x88x9210 and about +5.
The acid, when applied concurrently with the film former, should be sufficiently soluble in the film former and in a sufficient amount (including any optional cosolvents that are present in the film former) to provide the desired degree of adhesion for the particular hard tissue and application involved. For example, on dentin the degree of adhesion preferably is sufficient to provide an average measured shear strength of at least 7 MPa., and more preferably at least 12 MPa. Preferably, on dentin the degree of adhesion is sufficient to provide an average measured shear strength in a humid environment (i.e., as tested in a room temperature humidity chamber with a relative humidity greater than about 90%) of at least 5 MPa., more preferably at least 7 MPa, and most preferably at least 12 MPa.
Preferably, the calcium salt of the acid is also soluble in the film former (including any optional cosolvents that are present in the film former) or in the etchant solution (e.g., when the acid is applied sequentially with the film former). Acids having insoluble calcium salts may also be used in the primers of the present invention. For example, when the acid and film former are applied sequentially the acid may form insoluble calcium salt(s) that are insoluble in: the optional cosolvent; the subsequently applied film former (including any optional cosolvents that are present in the film former); or both. However, these salt(s) can be rinsed from the hard tissue, prior to application of the film former, to thereby not detrimentally affect the adhesion.
A xe2x80x9csolublexe2x80x9d acid or calcium salt of an acid, as used herein, is an acid or salt that when mixed with the film former (including any optional cosolvents that are present in the film former) under the desired conditions of use dissolves to form a homogeneous liquid mixture. Such conditions of use include temperature (e.g., body temperature), time (e.g., xe2x80x9cstanding timexe2x80x9d, that is, the amount of time the primer is allowed to remain on the surface of the hard tissue before hardening of the film former), and concentration (e.g., the concentration of acid and of calcium salt that may be formed in the film former when primer is applied to calcium-containing hard tissue such as teeth or bones). Alternatively, when the acid and film former are applied sequentially a xe2x80x9csolublexe2x80x9d acid or calcium salt of an acid, as used herein, is an acid or salt that when mixed with an optional cosolvent under the desired conditions of use dissolves to form a homogeneous liquid mixture.
The acid can be liquid or a solid; if a solid it should be dissolved in a suitable solvent to enable the acid to wet the hard tissue. Liquid acids can also be dissolved in a suitable solvent, e.g., in order to facilitate wetting. Preferred solvents for the acid are the film former cosolvents discussed in more detail below.
Suitable inorganic acids include HBr, HCl, and HNO3. Suitable organic acids include acetic acid, a-chloropropionic acid, 2-acrylamido-2-methylpropane sulfonic acid, acrylic acid, benzenesulfonic acid, benzoic acid, bromoacetic acid, 10-camphorquinonesulfonic acid, 10-camphorsulfonic acid, chloroacetic acid, citraconic acid, citric acid, dibromoacetic acid, dichloroacetic acid, di-Hema ester of 1,2,4,5 benzenetetracarboxylic acid, 2,4-dinitrophenol, formic acid, fumaric acid, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, maleic acid, methacrylic acid, 2-naphthalene sulfonic acid, nitric acid, oxalic acid, p-nitrophenol, phenol, phosphoric acid, phosphorous acid esters (such as 2,2xe2x80x2-bis(a-methacryloxy-b-hydroxypropoxyphenyl)propane diphosphonate (Bis-GMA diphosphonate), dibutyl phosphite, di-2-ethyl-hexyl phosphate, di-2-ethyl-hexyl phosphite, hydroxyethyl methacrylate monophosphate, glyceryl dimethacrylate phosphate, glyceryl-2-phosphate, glycerylphosphoric acid, methacryloxyethyl phosphate, pentaerythritol triacrylate monophosphate, pentaerythritol trimethacrylate monophosphate, dipentaerythritol petitaacrylate monophosphate, and dipentaerythritol pentamethacrylate monophosphate), pivalic acid, propionic acid, sulfuric acid, toluene sulfonic acid, tribromoacetic acid, trichloroaceiic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, and trihydroxybenzoic acid. Mixtures of such acids can be used if desired.
When the acid and film former are applied concurrently, then a preferred amount of acid to be dissolved in the film former will be between about 0.001M and the limit of solubility. The optimum amount depends in part on the pKa of the acid. For example, for sulfonic acids, concentrations between about 0.01M and about 0.5M are preferred. When the acid and film former are applied sequentially, then a preferred amount of acid to be dissolved in the cosolvent will be between about 0.001M and the limit of solubility. The optimum amount depends in part on the pKa of the acid.
The film former is a water-dispersible substance or water-dispersible mixture of substances, such substance(s) being organic monomers, oligomers, polymers, or cosolvents, wherein the film former contains at least one polymer prior to the hardening step, and is capable of forming a hardenable (e.g., polymerizable) continuous or semicontinuous film on the surface of the hard tissue. As used herein, a xe2x80x9cwater-dispersiblexe2x80x9d film former has a water dispersibility or more preferably a water solubility (exclusive of any water that may be present in the film former) of at least about 5 weight percent. Most preferably, the film former can be mixed with water in all proportions. For brevity, dispersible and soluble will sometimes be referred to collectively as dispersible. As used herein, xe2x80x9csolubilityxe2x80x9d means the capability of a substance to form a solution, i.e., either a true solution or a colloidal solution. A true solution being a uniformly dispersed mixture at the molecular or ionic level, of one or more substances (the solute) in one or more substances (the solvent). These two parts of a solution are called phases. A colloidal dispersion is often called a solution. Since colloidal particles are larger than molecules it is strictly incorrect to call such dispersions solutions; however this term is widely used in the literature. As used herein, xe2x80x9cdispersibilityxe2x80x9d means the capability of a substance to form a dispersion, i.e., a two-phase system where one phase consists of finely divided particles (often in the colloidal size range) distributed throughout a bulk substance, the particles being the disperse or internal phase and the bulk substance the continuous or external phase.
Preferred film formers contain one or more substances having a sufficient number of water-dispersing groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, cationic salts (e.g., ammonium, phosphonium or sulfonium groups), amide linkages or polyether linkages to render the film former water-dispersible. The film former, prior to removal of any volatile components, preferably wets the hard tissue and most preferably has a sufficiently low viscosity to enable it to flow into interstices that already exist in the surface of the tissue or that are created therein by the action of the acid. After removal of any volatile components the film former preferably has a sufficiently high viscosity to enable it to resist displacement by dentinal fluids or other extraneous liquids. To assist in hardening the film former, it preferably contains one or more polymerizable substances. Addition polymerizable substances (e.g., vinyl compounds such as acrylates and methacrylates) are especially preferred. The film former can also contain appropriate polymerization catalysts (e.g., photoinitiators) to assist in hardening the film former.
Suitable polymer components in the film former include linear, branched or cyclic polymers formed prior to the hardening step. For purposes of this invention, a polymer is a chemical compound having at least two repeat units. They can be polymers of ethylenically unsaturated monomers or they can be polymeric compounds like polyester, polyamide, polyether, polyethyleneglycol, polyethyleneglycol dimethacrylate and diacrylate, polysaccharide, cellulosic, polypropylene, polyacrylonitrile, polyurethane, poly(vinyl chloride), poly(methyl methacrylate), phenol-formaldehyde, melamine-formaldehyde, and urea-formaldehyde. Mixtures of such polymers can be used if desired.
Preferred polymers are the polymers of ethylenically unsaturated monomers. These polymers may be homo- or copolymers and may contain hydrophilic or hydrophobic groups. The polymer may optionally contain acid groups, their salts, or their reactive derivative groups. Particularly preferred polymers contain reactive groups that further react (i.e., crosslink or copolymerize) with the other components of the film former, the overcoat resin (i.e., the additional film former), or the dental restorative. Addition polymerizable reactive groups (e.g., vinyl groups such as acrylates and methacrylates) are especially preferred. Polymers of ethylenically unsaturated monomers are often used in dental glass ionomer cements. These polymers are especially useful in the present invention as they generally have good biocompatibility, are dispersible in water and have a suitable molecular weight. Particularly preferred polymers contain functional groups that have an affinity for the hard tissue. For example, such groups include xcex2-dicarbonyl groups and carboxylic acid groups. The polymer component of an ionomer cement is often a copolymer of acrylic acid and itaconic acid, although other monomers may be incorporated, and are herein referred to as polyalkenoic acids. See generally, Prosser et al., Developments in Ionic Polymersxe2x80x941, Chapter 5, Applied Science Publishers (London and New York, 1983). Recently such polymers have been further modified in the laboratory of the assignee of this invention by the incorporation of addition polymerizable reactive groups as mentioned above. Their preparation is described in European Patent Application No. 0 323 120 and in U.S. Pat. No. 5,130,347.
Suitable polymeric compounds of the invention have a weight average molecular weight prior to hardening of more than about 500, although preferably no greater than 2,000,000. More preferably, polymeric compounds of the invention have a weight average molecular weight prior to hardening of between about 1,000 and 1,000,000 evaluated against a polystyrene standard using gel permeation chromatography. Most preferably, polymeric compounds of the invention have a weight average molecular weight prior to hardening of between about 5,000 and 200,000.
Suitable monomer components in the film former include 2-hydroxyethylacrylate, 2-hydroxyethylmethacrylate (xe2x80x9cHEMAxe2x80x9d), 2- and 3-hydroxypropylacrylate and methacrylate, 1,3- and 2,3-dihydroxypropylacrylate and methacrylate, 2-hydroxypropyl-1,3-diacrylate and dimethacrylate, 3-hydroxypropyl-1,2-diacrylate and dimethylacrylate, pentaerythritol diacrylate and dimethacrylate, acrylic acid, methacrylic acid, 2-trimethylammonium ethylmethacrylic chloride, 2-acrylamido-2-methylpropane-sulfonic acid, acrylamide, methacrylamide, 2-hydroxyethylacrylamide and methacrylamide, N,N-bis(2-hydroxyethyl)acrylamide and methacrylamide, N-alkyl-N-hydroxyethyl acrylamides and methacrylamides, 2- and 3-hydroxypropylacrylamide and methacrylamide, methacrylamidopropyltrimethylammonium chloride, polyethyleneglycol (400) diacrylate and dimethacrylate, glycerol dimethacrylate and diacrylate, gylcerol monomethacrylate and monoacrylate, pentaerylthritol trimethacrylate and triacrylate, and mixtures thereof. It is expected that where an acrylate monomer is suitable the methacrylate analog will likewise be suitable.
The film former preferably comprises one or more suitable cosolvents. The cosolvent(s) aid in wetting the hard tissue and in solubilizing or dispersing the substances. Suitable cosolvents include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol, ketones such as acetone and methylethylketone, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, acrolein, glutaraldehyde and 2-hydroxy-adipaldehyde, amides such as acetamide and N,N-dimethylformamide, and other substances such as tetrahydrofuran and dimethyl sulfoxide. The film former preferably contains less than about 95 weight percent cosolvent, more preferably between about 15 and about 85 weight percent cosolvent.
The primer may contain only acid and film former. Other adjuvants such as polymerization catalysts, medicaments, fluoride compounds, indicators, dyes, wetting agents, buffering agents, thixotropes and the like can be included in the primer, contingent upon attainment of the desired degree of bonding performance and suitability for use on the desired hard tissue.
Hard tissue to which the primer is applied preferably is first cleaned using conventional methods (e.g., by abrading it with a bur), rinsed (e.g., using water) and dried (e.g., using air). If desired, deep excavations in teeth can be lined with a conventional basing material, (e.g., calcium hydroxide or a glass ionomer cement).
The acid and film former should be allowed to stand on the surface of the hard tissue long enough to provide the desired degree of priming. The standing time will depend upon the particular acid and film former employed, whether a concurrent or sequential application of acid and film former is employed, the type of hard tissue and its intended use, and the time available for carrying out the priming procedure. For priming dentin and enamel, standing times less than about 5 minutes, and preferably about 5 seconds to one minute provide very effective priming, although shorter or longer times can be used if desired.
As mentioned above, the primer preferably is overcoated with an optional layer of additional water-dispersible or water-indispersible film former, and then hardened. Preferably, such additional film former is copolymerizable with the residual film formed by removal of volatile cosolvents from the primer, and contains a polymerization catalyst (preferably a photoinitiator) capable of hardening the residual film and additional film former. If desired, the additional film former can contain conventional fillers, and can also contain adjuvants of the type described above. A particularly preferred additional film former is obtained by combining (1) the dimethacrylate (xe2x80x9cBis-GMAxe2x80x9d) derived from the reaction between methacrylic acid and the diglycidyl ether of bisphenol A with (2) a hydrophilic monomer such as HEMA, hydroxypropyl methacrylate, or methacrylic acid. Suitable monomers for use in the additional film former include the monomers described above as well as tetrahydrofurfural methacrylate, glyceryl-1,3-dimethacrylate, triethyleneglycol dimethacrylate, ethyl methacrylate, n-hexyl methacrylate, polyethyleneglycol dimethacrylate (xe2x80x9cPEGDMAxe2x80x9d), and 1,6-hexanediol dimethacrylate. Optionally, the additional film former may contain polymers of the type described above. The additional film former can also contain cosolvents of the type described above.
Polymerization catalysts that can be included in the primer or in the additional film former are autocure or light cure catalysts (i.e., catalysts which are sensitive to actinic radiation such as visible light) such as those mentioned in columns 28 and 29 of U.S. Pat. No. 4,539,382, chromophore-substituted halomethyl-s-triazines such as those shown in U.S. Pat. No. 3,954,475, chromophore-substituted halomethyl-oxadiozoles such as those shown in U.S. Pat. No. 4,212,970, and aryliodonium salts such as those shown in European Patent Application 0 290 133.
As also mentioned above, the primer and optional additional film former preferably are overcoated with a conventional restorative or coating. The hard tissue can then be finished using conventional techniques. For example, on tooth tissue, the primer can be overcoated with a dental adhesive, dental ionomer cement and/or a dental restorative and used, for example, to restore teeth, to install crowns, bridgework or other prosthetic devices, to bond orthodontic brackets to enamel, to seal pits and fissures or to veneer dentin, cementum or enamel. On bone and hoofs, the primer can be used in conjunction with a conventional filled or unfilled bone cement (e.g., a methyl methacrylate-based cement) to repair fractures or to fill defects. On fingernails, the primer can be used in conjunction with a conventional polymerizable fingernail coating to strengthen a fingernail, alter its shape, color or smoothness or fasten an artificial fingernail thereto.
The adhesive compositions of the present invention are particularly well suited for use in the high humidity environment of the mouth. Humidity values encountered in the mouth may fluctuate widely, depending on such factors as respiratory exhalation, fluid perfusion through the dentinal tubules and lack of control of extraneous fluids by the dental practitioner. When any of the above factors are present the hard tissue may be considered to be in a high humidity environment. Surprisingly, high adhesive shear strengths of restoratives on dental hard tissues may be achieved without the need to take extraordinary steps to protect the tissue from exposure to high humidity. For purposes of in-vitro comparisons, bond strength tests should preferably be compared in a room temperature high humidity chamber with a relative humidity greater than about 90%.
Adhesion to dentin or enamel of the primers of the invention was evaluated as follows:
First, teeth (usually five bovine teeth unless otherwise noted) of similar age and appearance were partially embedded in circular acrylic discs. The exposed portion of each tooth was ground flat and parallel to the acrylic disc using Grade 120 silicon carbide paper-backed abrasive mounted on a lapidary wheel, in order to expose the dentin or enamel. During this and subsequent grinding and polishing steps, the teeth were continuously rinsed with water. Further grinding and polishing of the teeth was carried out by mounting Grade 320 silicon carbide paper-backed abrasive and then Grade 600 silicon carbide paper-backed abrasive on the lapidary wheel. The polished teeth were stored in distilled water, and used for testing within 2 hours after polishing. The polished teeth were removed from the water and dried using a stream of compressed air.
Primer compositions were next applied to the prepared tooth surfaces as described in one of the following procedures:
Application Procedure Ixe2x80x94A single drop of primer composition (containing varying amounts of acid and film former) was painted onto each of the polished tooth surfaces with a brush and allowed to stand for 30 to 60 seconds. The primer was then blown dry with compressed air and cured using a 20-second irradiation with a xe2x80x9cVisilux(trademark) 2xe2x80x9d dental curing light (commercially available from 3M).
Application Procedure IIxe2x80x94A single drop of primer composition (containing varying amounts of acid and film former) was painted onto each of the polished tooth surfaces with a brush, allowed to stand for 30 to 60 seconds, and then blown dry with compressed air. An overcoat of additional water-dispersible or water-indispersible film former was applied, gently air thinned and cured using a 20-second irradiation with a Visilux 2 dental curing light.
Application Procedure IIIxe2x80x94An etchant was painted onto each of the polished tooth surfaces with a brush, allowed to stand for 15 seconds, and then blown dry with compressed air. A single drop of primer composition (containing varying amounts of acid and film former) was painted onto each of the polished tooth surfaces with a brush and immediately blown dry with compressed air. A thin layer of overcoat of additional water-dispersible or water-indispersible film former was painted onto each of the tooth surfaces, gently air thinned and cured using a 10-second irradiation with a Visilux 2 dental curing light.
Application Procedure IVxe2x80x94An etchant was painted onto each of the polished tooth surfaces with a brush, allowed to stand for 15 seconds (unless otherwise noted), rinsed with distilled water and then blown dry with compressed air. A single drop of primer composition (containing varying amounts of acid and film former) was painted onto each of the polished tooth surfaces with a brush and immediately blown dry with compressed air. A thin overcoat of additional water-dispersible or water-indispersible film former was painted onto each of the tooth surfaces, gently air thinned and cured using a 10-second irradiation with a Visilux 2 dental curing light.
Application Procedure Vxe2x80x94In a high humidity chamber (having a temperature of 25xc2x0 C. and a relative humidity greater than 90%) an etchant was painted onto each of the polished tooth surfaces with a brush, allowed to stand for 15 seconds (unless otherwise noted), rinsed with distilled water and then blown with compressed air. A single drop of primer composition (containing varying amounts of acid and film former) was painted onto each of the polished tooth surfaces with a brush and immediately blown with compressed air. A thin overcoat of additional water-dispersible or water-indispersible film former was painted onto each of the tooth surfaces, gently air thinned and cured using a 10-second irradiation with a Visilux 2 dental curing light.
Previously prepared molds made from a 2-mm thick xe2x80x9cTeflonxe2x80x9d sheet with a 4 mm diameter hole through the sheet were clamped to each prepared tooth so that the central axis of the hole in the mold was normal to the tooth surface. The hole in each mold was filled with a visible light-curable dental restorative (typically xe2x80x9cP50(trademark)xe2x80x9d brand universal shade restorative, available from 3M) and cured using a 20-second irradiation. It is believed that the choice of restorative might affect the bond strength values obtained for a given adhesive system. For example, some adhesive systems of the present invention provide very strong bonds to hard tissue that are believed to fail at the restorative-adhesive interface or within the restorative and not at the adhesive-hard tissue interface. A higher strength restorative may increase the measured bond strength for these adhesive systems. Therefore, comparisons between different adhesive systems should be made, wherever possible, using similar restorative systems. The teeth and molds were allowed to stand for about 5 minutes at room temperature, then stored in distilled water at 37xc2x0 C. for 24 hours unless otherwise noted. The molds were then carefully removed from the teeth, leaving a molded button of restorative attached to each tooth.
Adhesive strength was evaluated by mounting the acrylic disk in a holder clamped in the jaws of an xe2x80x9cInstronxe2x80x9d apparatus with the polished tooth surface oriented parallel to the direction of pull. A loop of orthodontic wire (0.44 mm diameter) was placed around the restorative button adjacent to the polished tooth surface. The ends of the orthodontic wire were clamped in the pulling jaw of the Instron apparatus, thereby placing the bond in shear stress. The bond was stressed until it (or the dentin or button) failed, using a crosshead speed of 2 mm/min.
The following examples are offered to aid in understanding of the present invention and are not to be construed as limiting the scope thereof. Unless otherwise indicated, all parts and percentages are by weight.